This proposal is a continuation of an ongoing program on the molecular aspects of the meiotic process in mammalian spermatocytes. It is a process which is critical to normal sperm development and also to normal genetic transmission. The main thrust of the research program is to clarify the biochemical factors which regulate and determine the mechanisms governing crossing-over between chromosomes. A substantial feature of the program derives from results obtained during the past two years in which it has been shown that a well defined metabolic program exists in the spermatocyte which is correlated with chromosome behavior during meiosis and in which it has also been shown that two distinctive proteins are present in the spermatocytes that can either separate or reanneal DNA strands. By isolating spermatocytes at different stages of meiosis it is possible to examine chromosomal constitution and protein activities of the spermatocytes as they develop to the spermatid stage. In so doing we wish to identify and characterize the different protein components that can form an "in vitro" recombination system. We also wish to clone meiotic-specific DNA sequences. By examining various chromosomally derived male steriles, we hope to resolve certain aspects of chromatin organization in relation to crossing-over.